A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for various applications. In particular, individual fuel cells can be stacked together in series to form a fuel cell stack capable of supplying a quantity of electricity sufficient to power an electric vehicle. Accordingly, the fuel cell has been identified as a potential alternative for a traditional internal-combustion engine used in modern vehicles.
A common type of fuel cell is known as a proton exchange membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: a cathode electrode, an anode electrode, and an electrolyte membrane. The electrodes typically include a finely divided catalyst, such as platinum, supported on carbon particles and mixed with an ionomer. The electrolyte membrane is disposed between the electrodes and is generally formed from a proton-conducting polymer such as Nafion® polymer, commercially available from E.I. du Pont de Nemours and Company, for example. The electrolyte membrane and electrodes are disposed between porous diffusion media (DM). The DM facilitates a delivery of gaseous reactants, typically hydrogen and oxygen, to the electrodes for an electrochemical fuel cell reaction. Generally, the catalyst is coated on the electrolyte membrane (CCM) to form a membrane-electrode-assembly (MEA). In another typical configuration, the DM is catalyst-coated (CCDM) to form the electrodes of the fuel cell.
The electrolyte membrane, electrodes, and DM are disposed between a pair of fuel cell plates and sealed with a gasket. When the electrolyte membrane, electrodes, and DM are assembled as a unit, for example, with other components such as the gasket and the like, the assembly is called a unitized electrode assembly (UEA).
Each fuel cell plate has an active region to which the gaseous reactants are delivered for distribution to the electrodes. The fuel cell plate also includes a feed region having flow channels configured to deliver the gaseous reactants from a supply source to the active region. The electrolyte membrane typically extends across the feed region and terminates at the gasket. The electrolyte membrane is employed to separate and inhibit an intermixing of the gaseous reactants. However, the DM is generally limited to the active region so that there is adequate space for the gaseous reactants to flow through the flow channels in the feed region. The fuel cell may also include metal shims or foils in the feed region that provide a stiffness to the electrolyte membrane and that militate against a blockage of the flow channels by the membrane.
The electrolyte membrane in the feed region is typically coated or laminated with a chemically inert material to inhibit a corrosion of the fuel cell plates that contact the electrolyte membrane. However, both the electrolyte membrane and the inert materials are prone to swelling. Swelling of the electrolyte membrane is known to cause flow channel blockage, delamination from the metal shims, and result in fuel cell instability. The electrolyte membrane also is generally not compatible with certain fuel cell or automotive fluids, such as coolants, grease, and oil, with which the electrolyte membrane may come into contact during operation. The electrolyte membrane that extends into the feed region or to an outer perimeter of the fuel cell is particularly susceptible to contamination with these types of fluids.
There is a continuing need for a fuel cell having an electrolyte membrane with optimized dimensions. Desirably, the optimized membrane dimensions increase fuel cell robustness and reliability. The optimized electrolyte membrane also desirably reduces the fuel cell complexity and cost and improves manufacturability of the fuel cell.